A vehicle fuel system typically has a fuel tank for holding a supply of liquid fuel for delivery to an engine. The fuel system also includes a lift or transfer pump for pumping fuel from the tank to the engine. Some engines, particularly those that have fuel injection, also have an injection pump that raises fuel pressure beyond that produced by the lift pump so that the fuel may be injected at high pressure into the combustion chambers of the engine.
Fuel filters are known for such fuel systems to remove contaminants such as dirt and water from the fuel before it reaches the engine. Fuel filters have been used in the fuel system either at the vacuum side or the pressure side of the fuel pump. Each position for the fuel filter in relation to the lift pump has advantages and disadvantages.
One filter assembly developed by the assignee of the present invention to overcome some of these disadvantages is shown in Hodgkins, U.S. patent application Ser. No. 08/512,352 filed Aug. 8, 1995 for "Double Pass Fuel Filter Assembly", now U.S. Pat. No. 5,922,199. This assembly includes a filter cartridge with first and second filter media loops, the second media loop surrounding the first media loop, and the first filter media loop providing primary filtration for fluid flowing from a first inlet port to a first outlet port. The second filter media loop, which is fluidly separated from the first filter media loop by a cup-shaped chamber, provides secondary filtration for fluid flowing from the second inlet port to a second outlet port.
According to the Hodgkins reference, the first inlet port of the assembly is connected to receive fuel from a tank, while the first outlet port is connected to supply filtered fuel to the inlet port of a lift pump. The outlet port of the lift pump is connected to the second inlet port in the assembly to receive the filtered fuel, while the second outlet port is connected to provide highly filtered fuel to the engine. The first media loop provides primary filtration for the fuel prior to being supplied to the lift pump, while the second media loop provides secondary (enhanced) filtration prior to being supplied to the fuel injection pump in the engine. Both filter media loops are replaced when the filter element is changed.
The Hodgkins filter assembly has the advantage of providing filtration prior to fuel passing to the lift pump. This minimizes the risk that large and potentially damaging impurities will reach the lift pump. The assembly also serves to remove large impurities before they are broken up or emulsified by the pumping action of the lift pump. These large impurities are captured in the first filter media loop and are periodically drained or dumped out of the assembly when the filter element is replaced. A further advantage is that by having fuel undergo primary filtration before reaching the lift pump, the life of the fine filter media in the secondary filter media loop is prolonged. A still further advantage is that the dual filtration is provided in a single filter assembly that is relatively small and easy to mount to the fuel lines.
While the Hodgkins filter assembly has many advantages over prior filter assemblies, the Hodgkins assembly is not appropriate for all applications, as it is generally designed for a specific head structure. That is, the filter head for the Hodgkins assembly includes all four ports to receive fuel for the two fuel paths through the element. The filter element is located in a canister that is attached with a locking ring to the underside of the filter head. To replace the filter element, the fuel in the canister must be initially drained through a drain port, the locking collar for the canister removed, the canister moved downwardly away from the head, and then the filter element removed from the canister. This can be awkward and time-consuming. In addition, any fuel remaining in the head can drip onto the hands of the user or onto the engine block when the canister is removed.
As such, it is believed there is a demand in the industry for a further improved filter assembly and element that provides dual fuel paths for enhanced filtration of fuel, and which provides easy access to and replacement of the filter element for the assembly, without time-consuming steps or spillage.